Acoustic Interface Device

ABSTRACT

A system is provided including an acoustic interface device, configured for coupling to a transducer and to a specimen, the acoustic interface device comprising a material composition having a shear wave attenuation coefficient a s  of at least about 5 dB/cm when subjected to an acoustic signal at a frequency between about 200 to 500 kHz. The acoustic interface device may be formed of polytetrafluoroethylene (Teflon®), a perfluoroalkoxy alkane (PFA), polycarbonate (Lexan®), or polyether ether ketone (PEEK). Methods of using the acoustic interface device with a transducer for ultrasonic measurement of a specimen are also disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

Not applicable.

TECHNICAL FIELD OF THE INVENTION

The present disclosure relates generally to systems, methods, andapparatuses using ultrasonic signals for measurement, testing or thelike, and more particularly, to an acoustic interface device for usewith the same.

BACKGROUND

Ultrasonic techniques are commonly used for non-destructive testing orevaluation (NDT or NDE) of materials, e.g., by measurement of propertiesof the material such as ultrasonic velocity and attenuation. One area inwhich such ultrasonic techniques are applied is the evaluation ofunderground/undersea geological formations for determining the presenceor absence of hydrocarbons (e.g., petroleum and natural gas) and theevaluation of the quality of casing and cement used in boreholes drilledin such underground/undersea geological formations for discovering andextracting such hydrocarbons.

In such ultrasonic techniques, transducers are commonly used to transmitacoustic signals into the specimen of interest (material under test) andto receive responses to the transmitted signals, e.g., reflections orechoes thereof, the characteristics of which are analyzed to yieldinformation about the properties of material under test. Under certainadverse conditions, e.g., under high temperature or pressure, in acorrosive environment, or when the specimen is very small, it is notfeasible to use a transducer in direct contact with the specimen. Suchadverse conditions may obtain in the underground/undersea explorationfor hydrocarbons described above.

One conventional way of mitigating or overcoming such adverse conditionsis by using a buffer rod between the transducer and the specimen. Thebuffer rod eliminates direct contact between the transducer and thespecimen and thus protects the transducer from the adverse conditionspresent in the specimen environment. When acoustic properties of thebuffer rod are known, these known properties in combination with theacoustic response can help in determining acoustic properties of thespecimen. However, buffer rods suffer from the problem of spurious(trailing) echoes that interfere with the signal of interest (theresponse signal described above) received by the transducer. As thesespurious echoes are caused at least in significant part by modeconversion at the buffer rod boundaries, they have been mitigated orovercome by making the buffer rod large, tapered, or grooved. However,such buffer rods are too large for accommodation in a downhole tool(e.g., a wireline or logging while drilling (LWD) tool) such as is usedin boreholes for exploring for hydrocarbons underground/undersea.

Accordingly, there is a need for improving the accuracy and sensitivityof ultrasonic techniques for evaluation of materials, such as with useof a buffer rod, where the techniques can be performed and the equipmentrequired therefor can be accommodated in a downhole tool.

SUMMARY

Systems, apparatuses and methods that use an acoustic interface deviceare provided. These systems, apparatuses and methods may improve theaccuracy and sensitivity of ultrasonic measurement techniques that maybe employed, inter alia, in a downhole environment.

According to a first aspect of the invention, there is provided a systemincluding an acoustic interface device, configured for coupling to atransducer and to a specimen. The acoustic interface device has amaterial composition having a shear wave attenuation coefficient α_(S)of at least about 5 dB/cm when subjected to an acoustic signal at afrequency between about 200 to 500 kHz.

According to a second aspect of the invention, there is provided asystem including an acoustic interface device, configured for couplingto a transducer and to a specimen. The acoustic interface device isformed from a material from the group consisting of:polytetrafluoroethylene (Teflon®), a perfluoroalkoxy alkane (PFA),polycarbonate (Lexan®), and polyether ether ketone (PEEK).

According to a third aspect of the invention, there is provided aprocess including the following operations: providing an acousticinterface device, coupled to a transducer; coupling the acousticinterface device to a specimen; by the transducer, generating a firstacoustic signal, such that the generated first acoustic signal istransmitted to the acoustic interface device; and receiving a secondacoustic signal in response to the transmitted first acoustic signal.The acoustic interface device has a material composition having a shearwave attenuation coefficient α_(S) of at least about 5 dB/cm whensubjected to an acoustic signal at a frequency between about 200 to 500kHz.

According to a fourth aspect of the invention, there is provided aprocess including the following operations: providing an acousticinterface device, coupled to a transducer; coupling the acousticinterface device to a specimen; by the transducer, generating a firstacoustic signal, such that the generated first acoustic signal istransmitted to the acoustic interface device; and receiving a secondacoustic signal in response to the transmitted first acoustic signal.The acoustic interface device is formed from a material from the groupconsisting of: polytetrafluoroethylene (Teflon®), a perfluoroalkoxyalkane (PFA), polycarbonate (Lexan®), and polyether ether ketone (PEEK).

BRIEF DESCRIPTION OF THE DRAWINGS

The following figures form part of the present specification and areincluded to further demonstrate certain aspects of the present claimedsubject matter, and should not be used to limit or define the presentclaimed subject matter. The present claimed subject matter may be betterunderstood by reference to one or more of these drawings in combinationwith the description of embodiments presented herein. Consequently, amore complete understanding of the present embodiments and furtherfeatures and advantages thereof may be acquired by referring to thefollowing description taken in conjunction with the accompanyingdrawings, in which like reference numerals may identify like elements,wherein:

FIG. 1 illustrates a measurement cell for ultrasonic testing of a fluid,according to some embodiments;

FIG. 2 illustrates acoustic interface devices of different sizes andshapes, which may be used in a measurement cell, according to someembodiments;

FIG. 3 illustrates a measurement cell for ultrasonic testing of a fluid,suitable for use in a logging while drilling (LWD) tool, according tosome embodiments;

FIG. 4 illustrates an LWD tool containing the measurement cell of FIG.3, according to some embodiments;

FIG. 5 illustrates a measurement cell for ultrasonic testing of a fluid,suitable for use in a wireline tool, according to some embodiments;

FIG. 6 illustrates a wireline tool containing the measurement cell ofFIG. 5, according to some embodiments;

FIG. 7 illustrates a graph of an acoustic waveform (signal amplitudeversus time) showing reflections of an acoustic signal that wastransmitted into a specimen via an acoustic interface device, accordingto some embodiments;

FIG. 8 illustrates four graphs, each graph being of a respectiveacoustic waveform (signal amplitude versus time) showing reflections ofan acoustic signal transmitted into a respective buffer rod, where eachbuffer rod has a respective one of four different material compositions;

FIG. 9A illustrates a graph showing an acoustic waveform (signalamplitude versus time) showing reflections of an acoustic signaltransmitted into an acoustic interface device formed of Teflon®,according to some embodiments; FIG. 9B illustrates a graph showing theFast Fourier Transform (FFT) spectrum of a portion of the waveform ofFIG. 9A, according to some embodiments; and FIG. 9C illustrates a graphshowing the group delay spectrum of a portion of the waveform of FIG.9A, according to some embodiments;

FIGS. 10A-10D illustrate respectively four different spatialarrangements of a transducer and an acoustic interface device, and FIGS.10E-H illustrate respective graphs showing acoustic waveforms (signalamplitude versus time) of pulse-echo responses corresponding to thearrangements of FIGS. 10A-D, respectively, according to someembodiments;

FIG. 11 is a block diagram of an ultrasonic measurement system,according to some embodiments; and

FIG. 12 is a flowchart illustrating a method for performing ultrasonictesting of a specimen using an acoustic interface device, according tosome embodiments.

NOTATION AND NOMENCLATURE

Certain terms are used throughout the following description and claimsto refer to particular system components and configurations. As oneskilled in the art will appreciate, the same component may be referredto by different names. This document does not intend to distinguishbetween components that differ in name but not function. In thefollowing discussion and in the claims, the terms “including” (and thelike) and “comprising” (and the like) are used in an open-ended fashion,and thus should be interpreted to mean “including, but not limited to .. . . ”

The term “couple” and cognate terms as used herein in the context ofultrasonic testing are to be construed broadly as encompassing any kindof coupling, including, as non-limiting examples, (i) coupling involvingthe use of a coupling medium (which could be air or another medium,e.g., an oil or gel) between the elements to be coupled, (ii) couplingby bonding together the elements to be coupled, e.g., using an adhesive,and (iii) coupling by disposing the elements to be coupled in directcontact with each other, without the use of any coupling medium.

DETAILED DESCRIPTION

The foregoing description of the figures is provided for the convenienceof the reader. It should be understood, however, that the embodimentspresented herein are not limited to the precise arrangements andconfigurations shown in the figures. Also, the figures are notnecessarily drawn to scale, and certain features may be shownexaggerated in scale or in generalized or schematic form, in theinterest of clarity and conciseness. Relatedly, certain features may beomitted in certain figures, and this may not be explicitly noted in allcases.

While various embodiments are described herein, it should be appreciatedthat the present invention encompasses many inventive concepts that maybe embodied in a wide variety of contexts. The following detaileddescription of exemplary embodiments, read in conjunction with theaccompanying drawings, is merely illustrative and is not to be taken aslimiting the scope of the invention, as it would be impossible orimpractical to include all of the possible embodiments and contexts ofthe invention in this disclosure. Upon reading this disclosure, manyalternative embodiments of the present invention will be apparent topersons of ordinary skill in the art. The scope of the invention isdefined by the appended claims and equivalents thereof.

Illustrative embodiments of the invention are described below. In theinterest of clarity, not all features of an actual implementation aredescribed or illustrated in this specification. In the development ofany such actual embodiment, numerous implementation-specific decisionsmay need to be made to achieve the design-specific goals, which may varyfrom one implementation to another. It will be appreciated that such adevelopment effort, while possibly complex and time-consuming, wouldnevertheless be a routine undertaking for persons of ordinary skill inthe art having the benefit of this disclosure.

In the following, a description is given of acoustic interface devices,and of measurement cells in which acoustic interface devices may beused, for ultrasonic testing, according to some embodiments. Theorganization of the following description is generally to set forthfirst the structure of the components and systems, and thereafter theoperation and use thereof. Thus, the structure may be presentedinitially in a manner that omits details of the context of operation anduse, and the subsequent description of operation and use may serve toclarify and contextualize aspects of the structure.

FIG. 1 is a schematic illustration of a measurement (or test) cell (orchamber) 100 for ultrasonic testing of a specimen or material undertest, which may be a fluid 101, according to some embodiments. Inaddition to holding fluid 101, measurement cell 100 includes atransducer 102, which may be a piezoelectric transducer. Examples ofsuch a transducer include the following: a 250 kHz 70% bandwidthpiezo-composite transducer (circular, rectangular or oval shaped); and a500 kHz wideband 1″ diameter transducer, such as the immersion type V301by Olympus. More generally, transducer 102 may be a transducer that isoperable to generate acoustic signals at least at a frequency betweenabout 200 to 500 kHz in response to an applied electric voltage.

Measurement cell 100 further includes an acoustic interface device 104.Acoustic interface device 104 may have the shape of a cylinder, squareplate, or another shape. As shown, acoustic interface device 104 mayinterface at a proximal end thereof (upper end in FIG. 1) withtransducer 102 and may function, e.g., as a buffer rod, noise dampenerand/or delay line. Further description of the structure and operation ofacoustic interface device 104 will be provided below, in part withreference to FIG. 2. The interface (coupling) between transducer 102 andacoustic interface device 104 may be achieved in any suitable manner, aswill be understood by one of ordinary skill in the art. For example,this interface may be achieved by coupling using a coupling medium,e.g., an oil, a gel, an epoxy, etc. As another example, this interfaceor coupling may be achieved by bonding the transducer to the acousticinterface device using, e.g., an epoxy bond.

Measurement cell 100 further includes a spacer 106 and a reflector 108.Reflector 108 may be a stainless steel plate (having an impedance ofapproximately 45 MRayls), or it may be made of another suitable materialthat has an acoustic impedance significantly higher than that of thefluid being tested (which is typically 1.5 to 3 MRayls), for example,corrosion resistant metals such as titanium (25 MRayls) or Inconel® (55MRayls) or even a tungsten loaded epoxy (9.5 MRayls for 25% tungsten byvolume in EPO-TEK 301®). The stainless steel reflector is preferably atleast 4.0 inch in thickness to reduce ringing and to delay reflectionsin the steel, which reflections might interfere with the signal ofinterest.

Spacer 106 may include multiple component spacers, as illustrated inFIG. 1. For convenience, spacer 106 may be referred to herein in eitherthe singular or the plural, it being understood that the singular mayrefer collectively to multiple component spacers. As shown, spacer 106may interface with acoustic interface device 104 at a proximal end ofspacer 106 (upper end in FIG. 1) and a distal end of acoustic interfacedevice 104 (lower end in FIG. 1). Further, as shown, spacer 106 mayinterface with acoustic interface device 104 over only a portion of thedistal end of acoustic interface device 104, e.g., at peripheral regionsof acoustic interface device 104 (lower end in FIG. 1). As furthershown, spacer 106 may interface with reflector 108 at a distal end ofspacer 106 (lower end in FIG. 1) and a proximal end of reflector 108(upper end in FIG. 1). In the arrangement described, spacer 106 may beattached to acoustic interface device 104 and to reflector 108 bysuitable means known to one of ordinary skill in the art.

In the arrangement described, as illustrated, spacer 106 provides for afluid gap 111 between (distal end of) acoustic interface device 104 and(proximal end of) reflector 108, in which fluid 101 freely flows to fillfluid gap 111. (FIG. 1 may be understood to be a cross-section taken inthe y-direction. The region identified as fluid gap 111 is in fluidcommunication with the regions at the right and left sides ofmeasurement cell 100 identified as containing fluid 101, but this fluidcommunication between these regions is not visible due to thetwo-dimensional nature of the figure. In this regard, if the setup shownin the figure were construed as two-dimensional it would appear as ifspacers 106 form a physical barrier between fluid gap 111 and theregions at the right and left sides of measurement cell 100 identifiedas containing fluid 101, which barrier would prevent fluid communicationtherebetween.) The extent of fluid gap 111 in the y-direction is d.Spacer 106 maintains this fixed distance d between (distal end of)acoustic interface device 104 and (proximal end of) reflector 108.

Acoustic interface device 104 may be partly immersed in fluid 101 influid gap 111. As a non-limiting example, about half of the height ofacoustic interface device 104 may be immersed, although FIG. 1 showsthat the level of fluid 101 reaches higher than the midpoint of theheight of acoustic interface device 104. (The height of acousticinterface device 104 refers to its extent in the y-direction in FIG. 1,in other words, the distance from its distal end at spacer 106 to itsproximal end at transducer 102. In a context other than that of FIG. 1,what is referred to here as the height of acoustic interface device 104may be referred to as its length.)

Reflector 108 serves to reflect acoustic waves that have beentransmitted from transducer 102 and have traveled through acousticinterface device 104 and fluid 101 in fluid gap 111 (or that have beenreflected at the interface of acoustic interface device 104 and fluid101 in fluid gap 111). Acoustic waves reaching reflector 108 arereflected back through fluid 101 in fluid gap 111 in the direction ofacoustic interface device 104 (upward in FIG. 1), and some of theseacoustic waves travel through acoustic interface device 104 and reachtransducer 102. The behavior of the acoustic waves is described infurther detail below in the context of the operation and use ofmeasurement cell 100.

Dimensions of components and aspects of the arrangement described abovemay be as follows. Transducer 102 may have an oval shape with a lengthof 1.65 inches, a width of 0.75 inches and a thickness (height inFIG. 1) of 1.25 inches. Alternatively, transducer 102 may be a typicalone inch diameter transducer, with a thickness (height in FIG. 1) of,e.g., 1.25 inches. Acoustic interface device 104 may have dimensionssimilar to these dimensions of transducer 102. Some exemplaryconfigurations (size and shape) of acoustic interface device 104 areseen in FIG. 2, which illustrates acoustic interface devices ofdifferent sizes and shapes, which may be used in a measurement cell,according to some embodiments. As seen in FIG. 2: an acoustic interfacedevice 204 a is a square plate of the following dimensions: 6.0 inchesin length, 6.0 inches in width, and 2.0 inches in thickness (height); anacoustic interface device 204 b is a tapered, grooved cylinder of thefollowing dimensions: 1.75 inches in minimum outer diameter, 2.125inches in maximum outer diameter, and 2.0 inches in height (the tapered,grooved cylinder has ten grooves with a slot width of 0.094 inches andslot depth of 0.063 inches); an acoustic interface device 204 c is atapered cylinder of the following dimensions: 1.75 inches in minimumouter diameter, 2.125 inches in maximum outer diameter, and 2.0 inchesin height; an acoustic interface device 204 d is a cylinder of thefollowing dimensions: 1.75 inches in diameter and 1.75 inches in height;and an acoustic interface device 204 e is a cylinder of the followingdimensions: 1.625 inches in diameter and 1.25 inches in height. Otherexemplary configurations of acoustic interface device 104 not shown inFIG. 2 are cylinders of the following dimensions: 1.75 inches indiameter and 2.0 inches in height; 2.0 inches in diameter and 2.0 inchesin height; 3.125 inches in diameter and 2.0 inches in height. Othershapes and sizes of acoustic interface device 104 may also be employed.Turning back to FIG. 1, exemplary dimensions of reflector 108 are: adiameter of 2.0 inches and a height of preferably 4.0 inches or more.With regard to fluid gap 111, the distance d (extending in they-direction in FIG. 1) may be, e.g., 10 mm, 19 mm, 20 mm, or anothermagnitude. As will be appreciated by one of skill in the art, dimensionsother than those set forth herein may be employed. Accordingly, thedimensions given herein are merely exemplary in nature and should not betaken as so limiting the invention. Also, dimensions listed above may beapproximations.

As will be understood, not all aspects of measurement cell 100 arenecessarily shown in FIG. 1. One of ordinary skill in the art willunderstand that certain additions, substitutions and variations may bemade.

Measurement cell 100 may be thought of as a generalized measurement cell100 that may be used in or, if necessary, adapted to, any suitablecontext or environment. FIGS. 3 and 5 illustrate variants of measurementcell 100 for use in downhole tools. Measurement cell 100 or variantsthereof may also be used in uphole environments. Generally, thedescription of measurement cell 100 (including components thereof) givenabove applies also to the measurement cells of FIGS. 3 and 5 describedbelow, unless indicated otherwise, whether explicitly or by logicalimplication of the description as a whole in light of the knowledge ofone of ordinary skill in the art. Accordingly, for convenience, not allaspects of measurement cell 100 that apply to the measurement cells ofFIGS. 3 and 5 are necessarily repeated in the description of the latter.It is noted, however, that the measurement cells of FIGS. 3 and 5 are insome respects described in greater detail than is measurement cell 100,and such detail is generally applicable to measurement cell 100 unlessindicated otherwise, whether explicitly or by logical implication of thedescription as a whole in light of the knowledge of one of ordinaryskill in the art.

It is noted that measurement cell 100 and the measurement cells of FIGS.3 and 5, including the components of these cells, may be designed to beoperable under at least the following conditions: between temperaturesof about 150 and 200 degrees Celsius, inclusive; and at pressuresbetween about 20,000 and 35,000 psi, inclusive.

FIG. 3 is a schematic illustration of a measurement cell 300 (enlargedview) for use in a logging while drilling (LWD) tool, while FIG. 4 is aschematic illustration of a portion of an LWD tool in a borehole, thetool containing measurement cell 300 (reduced, inset view). FIG. 4illustrates a cross-section taken in the vertical or axial direction ofthe generally cylindrical borehole and tool. Accordingly, the structuresshown in FIG. 4 exhibit a left-right symmetry about the hollow center ofthe tool, except for measurement cell 300, which is located on one sideof the tool. With reference to FIG. 4, LWD collar (drill collar) 490extends downward in a borehole, which has been bored in formation 491.The portion of the borehole surrounding LWD collar 490 is referred to asa borehole annulus 493. Mud (drilling fluid) flows into the hollowcenter of the LWD tool, downward, at arrow 495, and returns, upward, tothe surface, in borehole annulus 493 at arrows 497. A portion of thecollar 490 is gouged out to accommodate measurement cell 300. Forconvenience, the elements of measurement cell 300 are identified only inFIG. 3.

Turning to FIG. 3, measurement cell 300 includes transducer 302,acoustic interface device 304 and reflector 308. Acoustic interfacedevice 304 may, but need not, be cylindrical, as depicted. Transducer302 includes piezoelectric element 310, transducer backing 312, andtransducer housing 314 (these transducer components were omitted fromFIG. 1 for convenience). A connector 316 and an electronic board 318 areprovided for applying electric (voltage) signals to transducer 302(these components were omitted from FIG. 1 for convenience). In responseto an applied voltage, transducer 302 generates acoustic waves. Theacoustic waves are transmitted (downward arrows in FIG. 3) throughacoustic interface device 304 and fluid 301 in fluid gap 311 and arereflected by reflector 308 (upward arrows in FIG. 3) back through fluid301 in fluid gap 311 and acoustic interface device 304 to transducer302. As explained with reference to FIG. 1, not all acoustic wavestravel these entire distances; some are reflected at the interfacebetween acoustic interface device 304 and fluid 301 in fluid gap 311.Accordingly, the depiction of the travel of the acoustic waves by thearrows in FIG. 3 is an oversimplification and does not purport to showthe full complexity thereof. The representation of the travel of theacoustic waves given by the arrows in FIG. 1 is applicable tomeasurement cell 300 and is more accurate. The behavior of the acousticwaves will be described below in the context of the operation and use ofthe measurement cells.

As seen in FIG. 3, fluid 301, which in this case is mud 497, flowsfreely between borehole annulus 493 and fluid gap 311. As measurementcell 300 is accommodated in a hollowed out portion of LWD collar 490, aportion 306 of LWD collar 490 serves as a spacer in this arrangement,such that a fixed distance d is maintained between acoustic interfacedevice 304 and reflector 308. (This portion 306 may be referred to asspacer 306.) Other structures or arrangements for spacer 306 may beemployed. Also, of note, as measurement cell 300 is accommodated in ahollowed out portion of LWD collar 490, in the case in which LWD collar490 is made of stainless steel or another suitable material, the surfaceof LWD collar 490 itself that is facing fluid gap 311 may serve asreflector 308. Again, other structures or arrangements for reflector 308may be employed.

As further illustrated in FIG. 3, an oil fill 320 is providedsurrounding transducer 302 and acoustic interface device 304, and asealing ring (o-ring) 322 is provided around the distal end of acousticinterface device 304 (i.e., where acoustic interface device 304interfaces with fluid 301 at fluid gap 311), to prevent entry of fluid301 into transducer 302 and acoustic interface device 304, because suchentry of fluid 301 could contaminate and damage those components. (Oilfill 320 and sealing ring (o-ring) 322 may be included in thearrangement of FIG. 1, but are omitted in that figure for convenience.)

FIG. 5 is a schematic illustration of a measurement cell 500 (enlargedview) for use in a wireline tool (and shown in a portion of suchwireline tool), while FIG. 6 is a schematic illustration of a wirelinetool for use in a borehole, the tool containing measurement cell 500(reduced, inset view). As with FIG. 4, so too FIG. 5 illustrates across-section taken in the vertical or axial direction of the generallycylindrical wireline tool.

With reference to FIG. 6, wireline tool 680 includes a cable 682 and acentralizer 684 for use in lowering wireline tool 680 into and raisingwireline tool 680 out of a borehole (not shown), which has been bored ina formation (not shown). Measurement cell 500 is accommodated in ahollow portion of wireline tool 680. Wireline tool 680 is provided witha mud flow window 686. Mud flow window 686 may have a cage-likestructure, and may be vertically centered at or near the level of fluidgap 511 (FIG. 5) when measurement cell 500 is seated in wireline tool680, such that mud may freely flow between the borehole and fluid gap511.

With reference to FIG. 5, measurement cell 500 may include a structureand arrangement of parts similar or identical to that of measurementcell 300 as described above, namely including, e.g., transducer 502,which includes piezoelectric element 510, transducer backing 512, andtransducer housing 514; connector 516; electronic board 518; acousticinterface device 504; oil fill 520; sealing ring 522; spacer 506;reflector 508; and fluid gap 511. Through mud flow window 686, fluid501, which in this case is mud, may flow freely into fluid gap 511 fromthe borehole and from fluid gap 511 into the borehole. As withmeasurement cell 300 in the LWD tool, so too in the case of measurementcell 500 in wireline tool 680, applicable portions of the tool itselfmay, but need not, serve as spacer 506 and reflector 508, respectively.In view of the correspondence of components (and their functions)between measurement cell 500 and measurement cell 300, the descriptionof measurement cell 300 given above is understood to apply generally tomeasurement cell 500.

Further description will now be given of acoustic interface devices 104,304, 504, a non-exhaustive set of example configurations (sizes andshapes) of which are illustrated in and described with reference to FIG.2. As this description applies to any and all of acoustic interfacedevices 104, 304 and 504, reference will be made to an acousticinterface device generally, without mention of specific referencenumbers. The material composition of the acoustic interface device maybe one of the following: polytetrafluoroethylene (Teflon®), aperfluoroalkoxy alkane (PFA), polycarbonate (Lexan®), and polyetherether ketone (PEEK). The higher operating temperature polymers arepreferred for downhole use. Alternatively, the material composition maybe a composite, which includes one or more of the preceding materialsand one or more additional materials. Such a composite could be a matrixof a first material that is loaded with a second material. The matrixmaterial may be continuous, while the loaded material may bediscontinuous, dispersed within the matrix. The loaded material may butneed not be in the form of particles. Examples of such compositematerial compositions of the acoustic interface device are: (i)carbon-filled Teflon® (Teflon® matrix loaded with carbon particles), and(ii) stainless steel filled Teflon® (e.g., about 20% stainless steel byvolume). Other particle-filled composites may also be employed; forexample, Teflon® filled with carbon, steel or bronze; or PEEK (orTorlon®) filled with Teflon.

More generally, the material composition of the acoustic interfacedevice may be one having a shear attenuation coefficient a_(s) of atleast about 5 dB/cm when subjected to an acoustic signal at a frequencybetween about 200 to 500 kHz (i.e., at least at some frequency withinthis range, not necessarily at every frequency within this range).Further, the material composition of the acoustic interface device maybe one having a compressional wave velocity V_(P) of at most about 1600m/s at a temperature between about 150 and 200 degrees Celsius and apressure between about 20,000 to 35,000 psi (i.e., at least at sometemperature, not necessarily at every temperature, within this range,and at least at some pressure, not necessarily at every pressure, withinthis range). Further, the material composition of the acoustic interfacedevice may be one having a shear wave velocity V_(S) of at most about1100 m/s at a temperature between about 150 and 200 degrees Celsius anda pressure between about 20,000 to 35,000 psi (i.e., at least at sometemperature, not necessarily at every temperature, within this range,and at least at some pressure, not necessarily at every pressure, withinthis range). Further, the material composition of the acoustic interfacedevice may be one having a compressional wave attenuation coefficientα_(C) of at most about 6 dB/cm when subjected to an acoustic signal at afrequency between about 200 to 500 kHz (i.e., at least at somefrequency, not necessarily at every frequency, within this range).

It will be noted that Teflon® was tested under certain conditions andreported to have a shear attenuation coefficient α_(S) of 23.2171 dB/cmat 1 MHz, which, assuming a linear variation with frequency, isapproximately 5.8 db/cm at 250 kHz, which is significantly higher thanthat of many other engineering materials, and a shear velocity V_(S) of441 m/s, which is significantly lower than that of many otherengineering materials. See M. V. M. S. Rao and K. J. Prasanna Lakshmi,“Shear-wave propagation in rocks and other lossy media: An experimentalstudy,” Current Science, Vol. 8, No. 25, Oct. 25, 2003, page 1224. Inaddition, the instant inventors have tested Teflon® and PFA found themto have a compressional (p-wave) velocity V_(P) of approximately1100-1300 m/s, which is lower than that of many other engineeringmaterials, and a compressional wave attenuation coefficient α_(C) of1.0-2.3 dB/cm over 150-400 kHz, which is low to moderate relative toother engineering materials. The significance of these properties isdiscussed below.

The acoustic interface device may serve any of several differentfunctions. One function of the acoustic interface device is that of abuffer rod, that is, to provide a buffer between the transducer and thespecimen of interest or material under test. Such a buffer may be usefulor necessary, for example, where the conditions of the specimen (orspecimen environment) are such as could damage the transducer, e.g.,high temperature or pressure, or corrosive liquid. A buffer rod may alsobe useful or needed in the case of a small sample size, in order toobtain good contact with the specimen of interest. The acousticinterface device may also serve the functions of signal conditioning andnoise damping. The acoustic interface device may also serve as a delayline. With shear waves significantly suppressed (due to the above-notedrelatively high shear wave attenuation), an acoustic interface deviceformed of a material having a preferred (low, as noted above)compressional velocity provides a longer time window for receipt/captureof the response signal, since the compressional wave signal returns fromthe specimen without much interference from the second reflection fromthe interface of the specimen and the acoustic interface device. (This“second reflection” is explained as follows: in FIG. 1, when r₁ arrivesat transducer 102 at V_(A), a portion of r₁ (not shown) is reflectedback in acoustic interface device 104, downward in FIG. 1, toward fluidgap 111. When this portion of r₁ reaches the interface between acousticinterface device 104 and fluid gap 111, a part of this portion of r₁ isreflected, upward in FIG. 1, back toward transducer 102 and arrives attransducer 102. This portion that arrives at transducer 102 is the“second reflection.”)

One problem with prior art buffer rods is that the acoustic signalgenerated by the transducer and transmitted through the rod, which is acompressional acoustic wave (p-wave), may strike the circumferentialedge of the rod and generate shear waves due to mode conversion at theboundary. These shear waves may overlap in time with the signal ofinterest (i.e., the reflection of the transmitted signal, explainedbelow) that is to be received by the transducer and measured. Theseshear waves thus constitute spurious (or trailing) echoes, in effect,noise, that degrade the signal of interest or the ability to capture andinterpret it (e.g., the signal-to-noise ratio). Thus, these spuriousechoes diminish the accuracy with which acoustic properties of thespecimen can be measured, and hence the quality of the information thatcan be obtained about the physical properties of the specimen/specimenenvironment (e.g., borehole casing/cement) under investigation. Asnoted, prior art efforts to mitigate this problem have included using alarge buffer rod for noise delay, and using a tapered and/or groovedbuffer rod to reduce generation of mode converted waves. However, theseprior art mitigations are generally not suitable for use in a downholetool, as, for example, the size of the buffer rod may not beaccommodated in the tool, due to the limited space inside the tool.

By virtue of using materials such as the specific materials andcompositions described above, or materials satisfying propertiesdescribed above, however, an acoustic interface device, which can serveas a buffer rod, may be fashioned that is sufficiently small to beaccommodated in a downhole tool (e.g., of a diameter and length (i.e.,height in FIGS. 1 and 3-6) similar to that of a transducer), and thatsignificantly reduces noise, e.g., spurious echoes and ringing noise.With such an acoustic interface device, a much cleaner signal ofinterest can be obtained, supporting enhanced signal sensitivity andaccuracy of measurement, so as to yield more accurate and reliableinformation of acoustic properties and associated physical features. Theimprovements in the determination of acoustic properties of a specimenand such associated information will be more fully understood in lightof the following discussion of the operation and use of the measurementcells described herein.

Operation and use of measurement cells 100, 300 and 500 will bediscussed with reference to FIG. 7. Again, as this discussion applies toany and all of measurement cells 100, 300 and 500, reference will bemade to a measurement cell generally, without mention of specificreference numbers. FIG. 7 illustrates a graph of an acoustic waveformshowing reflections of an acoustic signal that was transmitted into aspecimen via an acoustic interface device, according to someembodiments. On the graph, the y-axis indicates signal amplitude and thex-axis indicates time. A measurement cell such as described herein maybe used to measure/determine acoustic properties of a specimen ormaterial (e.g., a fluid) under test, e.g., the properties of acousticimpedance, sound velocity, and attenuation. In the context of (cemented,cased) boreholes, these properties may be used to obtain a cement bondlog (CBL), which may provide information regarding the thickness of thecasing, how well the cement is adhering to the casing, and the qualityand acoustic impedance of the cement behind the casing.

As will be understood from the arrangements of the measurement cellsdescribed herein, these cells may be used to conduct pulse-echomeasurements. In a pulse-echo measurement, a pulse (acoustic signal) istransmitted by the transducer, and reflections (echoes) of thetransmitted pulse are received by the transducer and measured. (In thisregard, it is noted that it is possible for a measurement cell describedherein to employ two separate transducers, one for transmitting acousticsignals and one for receiving reflections thereof. For example, thetransducer+acoustic-interface-device portion of the above-describedarrangements could be replaced by atransmitting-transducer+first-acoustic-interface-device+receiving-transducer+second-acoustic-interface-deviceportion.)

Using pulse-echo measurements, one method that can be used to obtainacoustic properties of the specimen is the multiple reflection method(MRM), also known as the ABC method, which was devised by E. P.Papadakis (“Buffer-Rod System for Ultrasonic Attenuation Measurements,”J. Acoust. Soc. Am. 44, 1437-1441, 1968). With reference to FIGS. 1 and7, initially a pulse P₀ (acoustic signal) is generated by transducer 102and transmitted through acoustic interface device 104 in the directionof the fluid 101 in fluid gap 111, which is also the direction of thereflector 108. When pulse P₀ arrives at the interface of acousticinterface device 104 and the fluid 101 in fluid gap 110, due to thedifference in acoustic impedance between acoustic interface device 104and fluid 101 in fluid gap 111, a portion t₁ of the signal P₀ istransmitted through fluid 101, continuing in the direction of reflector108, and a portion r₁ of the signal P₀ is reflected back in thedirection of acoustic interface device 104, returning in the directionof transducer 102, according to the well-known equations for acoustictransmission and reflection at a boundary between materials of differentacoustic impedances, which for normal incidence, gives the fraction ofreflected acoustic energy as [(Z₁−Z₂)/(Z₁+Z₂)]² and the correspondingfraction of transmitted energy as one minus the fraction of energyreflected when assuming no energy loss at the interface. The portion r₁returns to and is received by transducer 102, indicated as V_(A) in FIG.1 and as peak V_(A) in FIG. 7. The portion t₁ reaches reflector 108 andis reflected back (for clarity relabeled as portion r₂) in the directionof acoustic interface device 104, which is also the direction oftransducer 102. (In practice, reflector 108 will not reflect 100% ofportion t₁; some of portion t₁ may be transmitted through reflector 108or dissipated.) When portion r₂ reaches the interface of acousticinterface device 104 and the fluid 101 in fluid gap 110, a portion of r₂is transmitted through acoustic interface device 104 (as portion t₂),continuing in the direction of transducer 102, and a portion of r₂ isreflected back (as portion r₃) in the direction of reflector 108. Theportion t₂ returns to and is received by transducer 102, indicated asV_(B) in FIG. 1 and as peak V_(B) in FIG. 7. The portion r₃ reachesreflector 108 and is reflected back (as portion r₄) in the direction ofacoustic interface device 104, which is also the direction of transducer102. (In practice, reflector 108 will not reflect 100% of portion r₃;some of portion r₃ may be transmitted through reflector 108 ordissipated.)

When portion r₄ reaches the interface of acoustic interface device 104and the fluid 101 in fluid gap 110, a portion of r₄ is transmittedthrough acoustic interface device 104 (as portion t₃), continuing in thedirection of transducer 102, and a portion of r₄ is reflected back (notshown) in the direction of reflector 108. The portion t₃ returns to andis received by transducer 102, indicated as V_(C) in FIG. 1 and as peakV_(C) in FIG. 7. The processes of reflection and transmission continueuntil the signal is completely absorbed or dissipated.

The amplitudes, and the arrival times at transducer 102, of peaks V_(A),V_(B) and V_(C) are measured (described below). The reflectioncoefficient R, which is a measure of how much of the signal isreflected, is obtained using Equation (1):

R=±(|1−(V _(B) ² /V _(A) V _(C))|)^(−0.5)   (1)

Given R, the acoustic impedance of fluid 101 in fluid gap 111, Z_(f) iscalculated using Equation (2):

Z _(f) =Z _(aid)(1+R)/(1−R)   (2)

where Z_(aid) is the acoustic impedance of acoustic interface device104, which is known.

The sound velocity of fluid 101 in fluid gap 111, c, is calculated asthe distance traveled by the acoustic signal (P₀ and as subsequentlyrenamed, as described above) divided by the travel time. It can be seenthat the acoustic signal travels a distance 2d (FIG. 1) in the timeinterval DT1 or DT2 (FIG. 7). This may be explained as follows. Theacoustic signal arrives at V_(A) (FIG. 1) at the starting point (leftside) of interval DT1 (FIG. 7). The acoustic signal arrives at V_(B)(FIG. 1) at the end point (right side) of interval DT1 (FIG. 7). Thedistance traveled by the acoustic signal during the time interval DT1 is2d, because the distance traveled by the acoustic signal at V_(B)(FIG. 1) exceeds the distance traveled by the acoustic signal at V_(A)(FIG. 1) by 2d. This is seen as follows. The distance traveled by thesignal from its start (initial transmission of P₀) to V_(A) (FIG. 1)equals the distance (seen in FIG. 1) represented by the portion labeledP₀ plus the distance (seen in FIG. 1) represented by the portion labeledr₁. The distance traveled by the signal from its start (initialtransmission of P₀) to V_(B) (FIG. 1) equals the distance (seen inFIG. 1) represented by the portion labeled P₀ plus the distance (seen inFIG. 1) represented by the portion labeled t_(i) plus the distance (seenin FIG. 1) represented by the portion labeled r₂ plus the distance (seenin FIG. 1) represented by the portion labeled t₂. Since the distance(seen in FIG. 1) represented by the portion labeled t₂ equals thedistance (seen in FIG. 1) represented by the portion labeled r₁, thedifference between the distance traveled by the signal from its start toV_(B) (FIG. 1) and the distance traveled by the signal from its start toV_(A) (FIG. 1) equals the distance (seen in FIG. 1) represented by theportion labeled t₁ (which is d) plus the distance (seen in FIG. 1)represented by the portion labeled r₂ (which is d), or in other words,2d. A comparable derivation can be performed to show that the distancetraveled by the acoustic signal over the time interval DT2 is 2d,because the distance traveled by the acoustic signal at V_(C) (FIG. 1)exceeds the distance traveled by the acoustic signal at V_(B) (FIG. 1)by 2d. Thus, the sound velocity (distance/time) of fluid 101 in fluidgap 111, c, is obtained from Equation (3), (4) or (5). Since DT1 and DT2are measured time intervals, due to practical limits of the accuracy ofmeasurement, they may differ from one another. To compensate for ormitigate this, the average of the sound velocity in the two intervalsDT1 and DT2 may be used, per Equation (5).

c=2d/DT1   (3)

c=2d/DT2   (4)

c=4d/(DT1+DT2)   (5)

Given Z_(f) and c, the density of fluid 101 in fluid gap 111 may becalculated by Equation (6).

Z_(f)=ρc   (6)

where ρ is the density of the fluid 101 in fluid gap 111.

Once the values of the acoustic properties of the fluid 101 are known,and, for example, compared at different times, inferences may be drawnfrom the values of these properties, or their change over time, as toconditions of interest of a cement bond log (CBL), e.g., informationregarding the thickness of the casing, how well the cement is adheringto the casing, and the quality of the cement behind the casing.

The improved quality of acoustic signals of interest obtained usingacoustic interface devices such as those described herein isdemonstrated in FIGS. 8, 9A-9C and 10A-10H.

FIG. 8 shows four pulse echo responses of a wideband 250-kHz transducer(oval, composite transducer, 1.65″ L×0.75″ W×1.25″ H) attached to fourbuffer rods, respectively, each formed of a different material. Theresponses are based on reflections from the rod-air interface at the farend of the rod (the end of the rod that is away from the transducer).The four materials, from top to bottom of the figure, are aluminum (2.0″L ×2.75″ diameter rod), glass (Corning® ULE, 3.0″ L×3.0″ diameter rod),epoxy (Duralco® 4460, 1.0″ L×3.0″ diameter rod), and Teflon® (2.0″L×3.125″ diameter rod). As clearly seen, the four waveforms differgreatly in signal quality. The rod of Teflon® material shows the bestsignal quality and the lowest ringing noises by far, among the fourmaterials tested. Note that beyond the initial noise, which all fourwaveforms have, the Teflon® material shows, relative to the others, avery flat waveform outside of the signal peaks of interest.

FIGS. 9A-9C shows pulse-echo responses from a wideband 250-kHztransducer (oval, composite transducer, 1.65″ L ×0.75″ W×1.25″ H)attached to a Teflon® acoustic interface device (which may serve as abuffer rod) of dimensions 2.0″ L×2.0″ diameter. Specifically, FIGS.9A-9C show respectively a raw waveform of the pulse echo response, anFFT spectrum of a portion of the pulse echo response, and a group delayspectrum of a portion of the pulse echo response.

In FIG. 9A, the waveform shows the main echo, which is the reflectionfrom the rear-air interface of the acoustic interface device, at about90 μs, with a second rear-air interface reflection echo at about 160 μs,and with little noise from about 100 μs to about 160 μs. FIG. 9B showsthe FFT spectrum, which has been processed from the windowed signal at80-140 μs, as indicated by the vertical lines in the graphs of FIGS. 9Aand 9B. As seen in FIG. 9B, the FFT spectrum is quite smooth, suggestingfew spurious modes or unwanted resonances were present. In FIG. 9C, thegroup delay (derivative of FFT phase to frequency) spectrum is seen tobe very smooth and flat over a wide frequency range of approx. 145-360kHz, indicating that only few spurious modes or other resonances arepresent in the Teflon® acoustic interface device and/or the transducer.

FIGS. 10A-10D illustrate respectively four different spatialarrangements of a transducer and an acoustic interface device(cylindrical or square plate), and FIGS. 10E-H illustrate respectivegraphs showing acoustic waveforms (signal amplitude versus time) ofpulse-echo responses corresponding to the arrangements of FIGS. 10A-D,respectively.

For FIGS. 10A-H, the transducer is a 250-kHz oval-shaped widebandtransducer. The pulse-echo responses are obtained as follows. Thetransducer transmits an acoustic signal through the acoustic interfacedevice and receives a response signal (reflection of the transmittedacoustic signal) from the rear end of the acoustic interface device,that is, the interface of the acoustic interface device and air.

In FIGS. 10A and 10B, the acoustic interface device 1004 a iscylindrical and has dimensions of 2.0″ diameter×2.0″ L, and is made ofTeflon® (referred to on the associated graphs of FIGS. 10E and 10F as“white Teflon®”). In FIG. 10A, transducer 1002 a is positioned at thecenter of acoustic interface device 1004 a. In FIG. 10B, transducer 1002a is positioned off-centered, near the edge (circumferential periphery)of the acoustic interface device 1004 a.

In FIGS. 10C and 10D, the acoustic interface device 1004 c is a squareplate and has dimensions of 2″ H×6″ W×6″ L, and is made of Teflon®filled with carbon particles (referred to on the associated graphs ofFIGS. 10G and 10H as “black Teflon®”). In FIG. 10C, transducer 1002 a ispositioned at the corner of acoustic interface device 1004 c. In FIG.10D, transducer 1002 a is positioned about 1.0″ closer to the center(compared to FIG. 10C), but still near the corner, of acoustic interfacedevice 1004 c, or about halfway from the corner to the center ofacoustic interface device 1004 c.

As for the pulse-echo responses, as seen in FIGS. 10E-10H, all four ofthe waveforms show almost identical pulse shape, amplitude, and traveltime of the main reflection echo at about 90 μs, as well as clean tailresponses up to around 170 μs. These responses demonstrate dominantp-wave signals and almost no spurious modes and little noise observed,despite different sizes of the acoustic interface device and differentpositions of the transducer with respect to the acoustic interfacedevice. In particular, it might have been thought that placing thetransducer close to the edge of the acoustic interface device wouldresult in increased spurious modes and noise, because it might have beenthought that the proximity of the transmitted signal to the edge of theacoustic interface device would result in increased mode conversion dueto the transmitted signal increasingly reaching the boundary of theacoustic interface device. The absence of increased spurious modes andnoise is understood to attest to the high rate of shear waveattenuation, and perhaps also to the slow shear wave velocity, of theTeflon® composition of the acoustic interface devices.

It will be understood that, with respect to FIGS. 8, 9A-9C and 10A-10H,the dimension L (length) mentioned with reference to a cylindricalacoustic interface device or buffer rod refers to the dimension referredto as height (the y-direction) in the discussion of FIGS. 1 and 3-6 andin the discussion of the cylindrical and cylindrical-type acousticinterface devices of FIG. 2.

Acoustic interface devices such as described herein may provideadvantages in ultrasonic measurement. Specifically, providing theacoustic interface device with a material composition having a highshear wave attenuation coefficient α_(S), a relatively low compressionalwave velocity V_(P), a low shear wave velocity V_(S), and/or amoderate-to-low compressional wave attenuation coefficient α_(C), suchas are possessed by the specific materials named herein or othercompositions, may provide advantages such as the following.

A high shear wave attenuation coefficient α_(S) may serve to attenuateshear waves generated, e.g., by mode conversion of the acoustic signalhitting the sidewalls (circumferential periphery) of the acousticinterface device. As a result, spurious (trailing) echoes (noise) may besignificantly reduced, providing a cleaner response signal of interest(e.g., increased signal-to-noise ratio). The cleaner response signal maypermit for increased accuracy of measurement, improved signal processingand interpretation, and increased sensitivity in measurement.

A relatively low compressional wave velocity V_(P) provides a relativelywide signal processing window before arrival of the second reflectionand hence may permit use of an acoustic interface device that is shorterthan prior art buffer rods. (This “second reflection” is explained asfollows: in FIG. 1, when r₁ arrives at transducer 102 at V_(A), aportion of r₁ (not shown) is reflected back in acoustic interface device104, downward in FIG. 1, toward fluid gap 111. When this portion of r₁reaches the interface between acoustic interface device 104 and fluidgap 111, a part of this portion of r₁ is reflected, upward in FIG. 1,back toward transducer 102 and arrives at transducer 102. This portionthat arrives at transducer 102 is the “second reflection.”) Unlike priorart buffer rods, an acoustic interface device of such short length mayfit inside downhole tools. (The dimension of length mentioned herecorresponds to the dimension of height in FIGS. 1 and 3-6 and in respectof the cylindrical acoustic interface devices of FIG. 2.)

A low shear wave velocity V_(S) may serve to eliminate noise in theresponse signal of interest and thus provide a cleaner signal, sincenoise in the form of (e.g., mode-converted or other) shear waves may besufficiently slow so as to interfere only to a small degree with theresponse signal of interest.

A moderate-to-low compressional wave attenuation coefficient a_(c) mayprovide for a strong response signal of interest (e.g., increasedsignal-to-noise ratio), since the signal may not be greatly weakenedprior to being measured.

As seen, all of the above properties generally contribute to achieving acleaner response signal of interest, e.g., decreased noise (spuriousechoes, ringing noise) and improved signal-to-noise ratio, and theattendant benefits.

One application or context of use for an acoustic interface device ormeasurement cell described herein is logging while tripping (LWT). Usingthe acoustic interface device or measurement cell, logging can beperformed during this time, which otherwise may not be able to beoptimally exploited and which may incur a significant cost assub-optimally productive time. In addition, an acoustic interface deviceor measurement cell described herein may be applicable to well loggingtools other than the LWD tool and wireline tool described above.

FIG. 11 is a block diagram of an ultrasonic measurement system, of whichmeasurement cell 100, 300 or 500 may be a part. Accordingly, ultrasonicmeasurement system 1100 includes a measurement cell, which is shownschematically in consonance with measurement cell 100 but which may bemeasurement cell 100, 300 or 500 or another measurement cell. Forconvenience, only some of the elements of the measurement cell in FIG.11 are identified, namely, transducer 1102, acoustic interface device1104, spacer 1106, reflector 1108, fluid gap 1111, and fluid 1101.Acoustic signals (as described above herein) are represented inoversimplified form by the dotted line and arrow. Ultrasonic measurementsystem 1100 may include a synchronization generator 1130, a pulsegenerator (pulser) 1132, a receiver 1134, an amplifier 1136, an A/Dconverter 1138, a computer 1140, and a display 1142. Synchronizationgenerator 1130 may generate trigger signals, e.g., at a high repetitionrate, to pulser 1132. In response to these trigger signals, pulser 1132provides electrical voltage to transducer 1102. In response to thisvoltage, transducer 1102 generates ultrasonic waves (acoustic signals),e.g., at the same repetition rate. The pulse-echo response (reflectedultrasonic waves, described hereinabove) is received by transducer 1102.In response to the received waves, transducer 1102 providescorresponding electrical voltage to receiver 1134. The received voltageis amplified by amplifier 1136, then converted from analog to digitalform by A/D converter 1138, and then processed and analyzed by computer1140. The amplified voltage is also transmitted from amplifier 1136 todisplay 1142 (e.g., an oscilloscope), on which it is displayed. Theconverted digital signal, as well as other associated outputinformation, may also be displayed on display 1142. Computer 1140 may beused for additional functions in ultrasonic measurement system 1100.

To be sure, as will be understood by one of ordinary skill in the art,variants of ultrasonic measurement system 1100 may be employed, e.g.,ultrasonic measurement system 1100 may include components in addition toor in substitution for components illustrated here, and may not includeall components illustrated here.

An example of one additional component that may be included inultrasonic measurement system 1100 is a filter, e.g., a high pass filteror a band pass filter (e.g., a 150-550 kHz band pass), which may be usedto filter the received acoustic signal in order to obtain a cleanerresponse signal of interest.

FIG. 12 is a flowchart illustrating an exemplary method 1200 forperforming ultrasonic testing of a specimen using an acoustic interfacedevice. According to method 1200, at step 1205, an acoustic interfacedevice is provided. At step 1210, the acoustic interface device iscoupled to a transducer. As an example, this coupling may be via acoupling medium, e.g., an oil, a gel, or an epoxy. As another example,this coupling may be achieved by bonding the transducer to the acousticinterface device using, e.g., an epoxy bond. Alternatively, thiscoupling may be achieved in any suitable manner, as will be understoodby one of ordinary skill in the art. At step 1215, the acousticinterface device is coupled to a specimen of interest or material undertest. The specimen of interest or material under test may but need notbe a fluid. At step 1220, a reflector is coupled to the specimen at afixed distance from the acoustic interface device. As an example, thesecouplings to the specimen (steps 1215 and 1220) may be by directcontact, without any coupling medium, or may be achieved in any suitablemanner, as will be understood by one of ordinary skill in the art. Atstep 1225, the transducer generates a first acoustic signal such thatthe generated first acoustic signal is transmitted to the acousticinterface device that is coupled to the transducer. At step 1230, asecond acoustic signal is received in response to the transmitted firstacoustic signal. This second acoustic signal (response signal) may be areflection of the transmitted first acoustic signal, as in a pulse-echoarrangement, and it may be received by the transducer, as describedhereinabove. (To avoid possible confusion, it is noted that this secondacoustic signal may refer to any one, or collectively to more than one,such reflection, e.g., any one or more of V_(A), V_(B), V_(C) (asdepicted) and further reflection echoes (as described in the instantdescription) with reference to FIGS. 1 and 7. This second acousticsignal is not to be taken as referring exclusively or necessarily to thesecond of those reflections, namely, V_(B). Nor is this second acousticsignal to be taken as referring exclusively or necessarily to the“second reflection” described above, that is, in FIG. 1, the portion ofr₁ that at V_(A) is reflected back from the transducer toward the fluidgap and then back from the fluid-gap-acoustic-interface-device-interfaceto the transducer.) In alternative embodiments employing athrough-transmission arrangement or a pitch-catch arrangement (describedimmediately below) rather than a pulse-echo arrangement, this secondacoustic signal may be a signal received by the receiver (e.g.,receiving transducer) from the specimen in response to the firstacoustic signal, which is transmitted by the transmitter (e.g.,transmitting transducer) into the specimen. At step 1235, one or moreacoustic properties are determined based on the received second acousticsignal(s). Such determination may be based also on or involve additionalinputs. It will be understood that further details pertaining to thepreceding steps, as well as indications of steps that may be added,substituted, reordered, omitted, or otherwise modified, have been setforth herein and will be appreciated by those of ordinary skill in theart.

One example of such variation of method 1200 would be omission of step1220. Such variation would be applicable to a through-transmissionarrangement or a pitch-catch arrangement rather than a pulse-echoarrangement. Each of a through-transmission arrangement and apitch-catch arrangement uses two transducers rather than one as may beused in pulse-echo measurement, as described above. Inthrough-transmission arrangement or pitch-catch arrangement, onetransducer transmits the acoustic signal into the specimen and anothertransducer receives the response signal from the specimen. The twotransducers may interface the specimen at different locations on thespecimen.

While the instant disclosure includes statements that may be understoodas offering reasons or explanations for certain phenomena or results,the instant inventors do not wish to be bound by theory.

In light of the principles and example embodiments described andillustrated herein, it will be recognized that the example embodimentscan be modified in arrangement and detail without departing from suchprinciples. Also, the foregoing discussion has focused on particularembodiments, but other configurations are also contemplated. Inparticular, even though expressions such as “in one embodiment,” “inanother embodiment,” or the like are used herein, these phrases aremeant to generally reference embodiment possibilities, and are notintended to limit the invention to particular embodiment configurations.As used herein, these terms may reference the same or differentembodiments that are combinable into other embodiments. As a rule, anyembodiment referenced herein is freely combinable with any one or moreof the other embodiments referenced herein, and any number of featuresof different embodiments are combinable with one another, unlessindicated otherwise or so dictated by the description herein in view ofthe knowledge of one or ordinary skill in the art.

Similarly, although example processes have been described with regard toparticular operations performed in a particular sequence, numerousmodifications could be applied to those processes to derive numerousalternative embodiments of the present invention. For example,alternative embodiments may include processes that use fewer than all ofthe disclosed operations, processes that use additional operations, andprocesses in which the individual operations disclosed herein arecombined, subdivided, rearranged, or otherwise altered.

This disclosure may include descriptions of various benefits andadvantages that may be provided by various embodiments. One, some, all,or different benefits or advantages may be provided by differentembodiments.

In view of the wide variety of useful permutations that may be readilyderived from the example embodiments described herein, this detaileddescription is intended to be illustrative only, and should not be takenas limiting the scope of this invention. What is claimed as theinvention, therefore, are all implementations that come within the scopeof the following claims, and all equivalents to such implementations.

What is claimed is:
 1. A system, comprising: an acoustic interfacedevice, configured for coupling to a transducer and to a specimen, theacoustic interface device comprising a material composition having ashear wave attenuation coefficient α_(S) of at least about 5 dB/cm whensubjected to an acoustic signal at a frequency between about 200 to 500kHz.
 2. The system of claim 1, wherein the material composition has acompressional wave velocity V_(P) of at most about 1600 m/s at atemperature between about 150 and 200 degrees Celsius and a pressurebetween about 20,000 to 35,000 psi.
 3. The system of claim 1, whereinthe material composition has a shear wave velocity V_(S) of at mostabout 1110 m/s at a temperature between about 150 and 200 degreesCelsius and a pressure between about 20,000 to 35,000 psi.
 4. The systemof claim 1, wherein the material composition has a compressional waveattenuation coefficient α_(C) of at most about 6 dB/cm when subjected toan acoustic signal at a frequency between about 200 to 500 kHz.
 5. Thesystem of claim 1, further comprising a transducer coupled to theacoustic interface device, wherein the transducer is a piezoelectrictransducer operable to generate an acoustic signal at least at afrequency between about 200 kHz and 500 kHz in response to an appliedelectric voltage.
 6. The system of claim 5, further comprising areflector, wherein the acoustic interface device comprises a proximalend and a distal end, wherein the acoustic interface device is coupledto the transducer at the proximal end, and the acoustic interface deviceis coupled to a specimen at the distal end, and wherein the reflector iscoupled to the specimen and disposed a fixed distance away from thedistal end.
 7. A system, comprising: an acoustic interface device,configured for coupling to a transducer and to a specimen, the acousticinterface device comprising a material from the group consisting of:polytetrafluoroethylene (Teflon®), a perfluoroalkoxy alkane (PFA),polycarbonate (Lexan®), and polyether ether ketone (PEEK).
 8. The systemof claim 7, wherein the acoustic interface device comprises aparticle-filled polytetrafluoroethylene (Teflon®) composite.
 9. Thesystem of claim 7, further comprising a transducer coupled to theacoustic interface device, wherein the transducer is a piezoelectrictransducer operable to generate an acoustic signal at least at afrequency between about 200 kHz and 500 kHz in response to an appliedelectric voltage.
 10. The system of claim 9, further comprising areflector, wherein the acoustic interface device comprises a proximalend and a distal end, wherein the acoustic interface device is coupledto the transducer at the proximal end, and the acoustic interface deviceis coupled to a specimen at the distal end, and wherein the reflector iscoupled to the specimen and disposed a fixed distance away from thedistal end.
 11. A method, comprising: providing an acoustic interfacedevice, coupled to a transducer; coupling the acoustic interface deviceto a specimen; by the transducer, generating a first acoustic signal,such that the generated first acoustic signal is transmitted to theacoustic interface device; and receiving a second acoustic signal inresponse to the transmitted first acoustic signal, wherein the acousticinterface device comprises a material composition having a shear waveattenuation coefficient a_(s) of at least about 5 dB/cm when subjectedto an acoustic signal at a frequency between about 200 to 500 kHz. 12.The method of claim 11, further comprising: coupling a reflector to thespecimen at a fixed distance from the acoustic interface device.
 13. Themethod of claim 11, further comprising: determining an acoustic propertyof the specimen based on the received second acoustic signal.
 14. Themethod of claim 11, wherein the material composition of the acousticinterface device has at least one property from the group consisting of:having a compressional wave velocity V_(P) of at most about 1600 m/s ata temperature between about 150 and 200 degrees Celsius and a pressurebetween about 20,000 to 35,000 psi; having a shear wave velocity V_(s)of at most about 1110 m/s at a temperature between about 150 and 200degrees Celsius and a pressure between about 20,000 to 35,000 psi; andhaving a compressional wave attenuation coefficient a_(c) of at mostabout 6 dB/cm when subjected to an acoustic signal at a frequencybetween about 200 to 500 kHz.
 15. The method of claim 11, wherein thespecimen is a liquid.
 16. A method, comprising: providing an acousticinterface device, coupled to a transducer; coupling the acousticinterface device to a specimen; by the transducer, generating a firstacoustic signal, such that the generated first acoustic signal istransmitted to the acoustic interface device; and receiving a secondacoustic signal in response to the transmitted first acoustic signal,wherein the acoustic interface device comprises a material from thegroup consisting of: polytetrafluoroethylene (Teflon®), aperfluoroalkoxy alkane (PFA), polycarbonate (Lexan®), and polyetherether ketone (PEEK).
 17. The method of claim 16, wherein the acousticinterface device comprises a particle-filled polytetrafluoroethylene(Teflon®) composite.
 18. The method of claim 16, further comprising:coupling a reflector to the specimen at a fixed distance from theacoustic interface device.
 19. The method of claim 16, furthercomprising: determining an acoustic property of the specimen based onthe received second acoustic signal.
 20. The method of claim 16, whereinthe specimen is a liquid.